1. Field of the Invention
The disclosed embodiments of the present invention relate to wireless communication.
2. Description of the Prior Art
In a wireless system, a performance of a transmitter strongly depends upon radio frequency (RF) gain blocks, high power amplifiers (HPAs), matching networks and other external components in a signal chain. Transmitters having identical wireless designs are expected to operate consistently in certain test cases. Unfortunately, almost no component provides very good absolute gain accuracy specifications and RF characteristics vary from device to device. In addition, a signal chain gain varies as the temperature and the frequency change.
The performance of the transmitter may be evaluated in terms of RF output power versus error-vector magnitude (EVM). Please refer to FIG. 1, which is a diagram illustrating respective relationships between respective output powers and EVMs of transmitters A, B and C. As shown in FIG. 1, the transmitter C may reach the lowest EVM (compared with the transmitters A and B) while the RF output powers are at the same level, and therefore, the performance of the transmitter C reaches the best. In other words, maximum output powers of the transmitters A, B and C are different to meet the transmitter specification (i.e. a transmitted signal is required to have an EVM less than a reference value).
Thus, there is a need for an innovative method to test and calibrate a transmitter in order to ensure a proper operating region of the transmitter to thereby provide a transmitted signal having a sufficiently high output power as well as good signal quality.